1. Field of the Invention
The present invention relates to methods and apparatus for forming a lateral wellbore in a well, more particularly the invention relates to the formation of lateral wellbores with greater efficiently and with fewer trips into the wellbore.
2. Background of the Related Art
The formation of lateral wellbores from a central cased wellbore is well known in the art. Lateral wellbores are typically formed to access an oil bearing formation adjacent the existing wellbore; provide a perforated production zone at a desired level; provide cement bonding between a small diameter casing and the adjacent formation; or to remove a loose joint of surface pipe. Lateral wellbores are advantageous because they allow an adjacent area of the formation to be accessed without the drilling of a separate wellbore from the surface. Any number of lateral wellbores may be formed in a well depending upon the needs and goals of the operator and the lateral wellbores can be lined with tubular like the main wellbore of the well from which they are formed.
The most well known method of forming a lateral wellbore uses a diverter or whipstock which is inserted into the main wellbore and fixed therein. The whipstock includes a concave, slanted portion which forms a surface for gradually directing a cutting device from the main wellbore of the well towards the wall of the wellbore where the lateral wellbore will be formed. The cutter is fixed at the end of a string of rotating pipe. Thereafter, an opening or “window” is formed in the wellbore casing as the cutter is guided through the wall by the whipstock. Forming a lateral wellbore with a whipstock assembly typically proceeds as follows: a whipstock assembly including an anchor portion therebelow is lowered into the well to the area below the point where the window is to be formed. The assembly is then fixed in the well with the anchor securely held within the wellbore casing. A drill string with a cutting tool disposed at the end thereof is then lowered into the well and the drill string and cutter are rotated in order to form the window in the wellbore. In some instances, the drill string and cutter can be installed in the well at the same time as the whipstock assembly by attaching the two with a shearable mechanical connection between the whipstock and the cutter. Thereafter, the cutter and drill string are removed from the well and the cutter is replaced with a drill bit. The drill string and drill bit are then lowered once more into the wellbore and the lateral wellbore is drilled using the conventional drill bit. After the lateral wellbore is formed, it is typically lined with its own casing which is subsequently cemented in place.
As the foregoing demonstrates, the formation of a lateral wellbore requires several separate pieces of equipment and more importantly, requires several trips into the well to either install or remove the downhole apparatus used to form the window or the lateral wellbore.
There are a number of apparatus currently available which, are designed to simplify or save time when performing operations in a wellbore. For example, a “mill/drill” is a special bit specifically designed to both mill through a casing and drill into a formation. Use of a mill/drill can eliminate the use of a separate mill and drill bit in a lateral wellbore operation and therefore eliminate the need to pull the mill out of the wellbore after forming the window in order to install the drill bit to form the lateral wellbore. Typically, the mill/drill includes materials of different physical characteristics designed to cut either the metallic material of the wellbore casing to form a window or designed to cut rock in formation material as the lateral wellbore is formed. In one example, inserts are installed in the drill bit whereby one set of inserts includes a durable cutting structure such as tungsten carbide for contacting and forming the window in the wellbore casing and a second set of inserts is formed of a harder material better suited for drilling through a subterranean formation, especially a rock formation. The first cutting structure is positioned outwardly relative to the second cutting structure so that the first cutting structure will mill through the metal casing while shielding the second cutting structure from contact with the casing. The first cutting structure can wear away while milling through the casing and upon initial contact with the rock formation, thereby exposing the second cutting structure to contact the rock formation. Combination milling and drill bits such as the foregoing are described in U.S. Pat. Nos. 5,979,571 and 5,887,668 and those patents are incorporated herein by reference in their entirety.
Another recent time saving improvement for downhole oil well operations involves the drilling of a wellbore using the tubular, or liner which will subsequently form the casing of the wellbore. This method of “drilling with liner” avoids the subsequent procedure of inserting liner into a previously drilled wellbore. In its simplest form, a drill bit is disposed at the end of a tubular that is of a sufficient diameter to line the wall of the borehole being formed by the drill at the end thereof. Once the borehole has been formed and the liner is ready to be cemented in the borehole, the drill bit at the end thereof is either removed or simply destroyed by the drilling of a subsequent, smaller diameter borehole.
Drilling with liner can typically be performed two ways: In the first method, the liner string itself with the drill bit fixed at the end thereof rotates. In a second method, the liner string is non-rotating and the drill bit, disposed at the end of the liner string and rotationally independent thereof, is rotated by a downhole motor or by another smaller diameter drill stem disposed within the liner that extends back and is rotated from the surface. In one example of a non-rotating liner, the bit includes radially extendable and retractable arms which extend outwards to a diameter greater than the tubular during drilling but are retractable through the inside diameter of the tubular whereby, when the wellbore is completed, the bit can be completely removed from the wellbore using a wireline device. The foregoing arrangement is described in U.S. Pat. No. 5,271,472 and that reference is incorporated herein in its entirety.
In another example of drilling with liner, a non-rotating tubular is used with a two-part bit having a portion rotating within the end of the tubular and another portion rotating around the outer diameter of the tubular. The rotation of each portion of the bit is made possible either by a downhole motor or by rotational force supplied to a separate drill stem from the surface of the well. In either case, the central portion of the bit can be removed after the wellbore has been formed. The liner remains in the wellbore to be cemented therein. A similar arrangement is described in U.S. Pat. No. 5,472,057 and that patent is incorporated herein by reference in its entirety.
Yet another emerging technology offering a savings of time and expense in drilling and creating wellbores, relates to rotary steerable drilling systems. These systems allow the direction of a wellbore to be changed in a predetermined manner as the wellbore is being formed. For example, in one well-known arrangement, a downhole motor having a joint within the motor housing can create a slight deviation in the direction of the wellbore as it is being drilled. Fluid-powered motors have been in use in drilling assemblies in the past. These designs typically utilize a fixed stator and a rotating rotor, which are powered by fluid flow based on the original principles developed by Moineau. Typical of such single-rotor, progressive cavity downhole motor designs used in drilling are U.S. Pat. Nos. 4,711,006 and 4,397,619, incorporated herein in their entirety. The stator in Moineau motors is built out of elastic material like rubber. Other designs have put single-rotor downhole power sections in several components in series, with each stage using a rotor connected to the rotor of the next stage. Typical of these designs are U.S. Pat. Nos. 4,011,917 and 4,764,094, incorporated herein in their entirety.
Another means of directional drilling includes the use rotary steerable drilling units with hydraulically operated pads formed on the exterior of a housing near the drill bit. The mechanism relies upon a MWD device (measuring while drilling) to sense gravity and use the magnetic fields of the earth. The pads are able to extend axially to provide a bias against the wall of a borehole or wellbore and thereby influence the direction of the drilling bit therebelow. Rotary steerable drilling is described in U.S. Pat. Nos. 5,553,679, 5,706,905 and 5,520,255 and those patents are incorporated herein by reference in their entirety.
Technology also exists for the expansion of tubulars in a wellbore whereby a tubular of a first diameter may be inserted into a wellbore and later expanded to a greater inside and outside diameter by an expansion tool run into the wellbore on a run-in string. The expansion tool is typically hydraulically powered and exerts a force on the inner surface of the tubular when actuated.
FIGS. 1 and 2 are perspective views of the expansion tool 100 and FIG. 3 is an exploded view thereof. The expansion tool 100 has a body 102 which is hollow and generally tubular with connectors 104 and 106 for connection to other components (not shown) of a downhole assembly. The connectors 104 and 106 are of a reduced diameter (compared to the outside diameter of the longitudinally central body part 108 of the tool 100), and together with three longitudinal flutes 110 on the central body part 108, allow the passage of fluids between the outside of the tool 100 and the interior of a tubular therearound (not shown). The central body part 108 has three lands 112 defined between the three flutes 110, each land 112 being formed with a respective recess 114 to hold a respective roller 116. Each of the recesses 114 has parallel sides and extends radially from the radially perforated tubular core 115 of the tool 100 to the exterior of the respective land 112. Each of the mutually identical rollers 116 is near-cylindrical and slightly barreled. Each of the rollers 116 is mounted by means of a bearing 118 at each end of the respective roller for rotation about a respective rotational axis which is parallel to the longitudinal axis of the tool 100 and radially offset therefrom at 120-degree mutual circumferential separations around the central body 108. The bearings 118 are formed as integral end members of radially slidable pistons 120, one piston 120 being slideably sealed within each radially extended recess 114. The inner end of each piston 120 (FIG. 3) is exposed to the pressure of fluid within the hollow core of the tool 100 by way of the radial perforations in the tubular core 115. In the embodiment shown in FIGS. 1–3, the expander tool is designed to be inserted in a tubular string. It can however, also be used at the end of a tubular string with fluid passing through it via ports formed in its lower end.
After a predetermined section of the tubular has been expanded to a greater diameter, the expansion tool can be deactivated and removed from the wellbore. Methods for expanding tubulars in a wellbore are described and claimed in Publication No. PCT/GB99/04225 and that publication is incorporated by reference in its entirety herein.
There is a need therefore for methods and apparatus for forming a lateral wellbore whereby subsequent trips into the main wellbore are minimized and wherein the wellbore can be formed in a faster, more efficient manner utilizing less time, equipment and personnel. There is a further need for a method of forming a lateral wellbore which utilizes various apparatus which have been developed for unrelated activities in a wellbore.